This invention relates to a method and apparatus for laying pipes in the ground and, more particularly, to the laying-in of pipes such as drainage, gas, water pipes, or cables of a relatively small diameter.
One of the more common ways of laying pipes into the ground is that trenches are dug, the pipes are then placed in the trench, and finally the trench is filled with earth. When a relatively large land space is available, no difficulty with this method of laying-in of the pipes exists. However, various problems arise when digging trenches in roads is carried out in big cities where sufficient land spaces are not available. More specifically, for instance, pavement must be destroyed and the trafic is obstructed in the course of construction.
Various attempts have heretofore been made to eliminate these problems by laying the pipes in the ground without digging the trenches. One such attempt has been to lay in the pipes when the excavated earth is discharged from the rear end of the laid-in pipes and another attempt has been to press the pipes into the ground upon consolidation of soil. A major difficulty with the first-mentioned attempt is that the scraped soil is removed from the rear end of the pipes by means for example of screw conveyors disposed within the pipes and, hence, the pipes are filled up with the scraped soil which is being discharged, with the results that the foremost point where the excavation is carried out can not be detected from a departure pit from which the pipes are laid in, and thus the straight advance of the laid-in pipes is difficult to maintain. Furthermore, since the scraped soil is discharged into the departure pit, installation of a jack for pressing the pipes to be laid in, and control equipment and the like within the departure pit is limited, and the earth hauling operation is interfered, thereby resulting in poor working efficiency. Later attempts to provide a detector pipe extending along the peripheral surface of and in parallel with the axis of the laid-in pipes so as to detect a vertical position of the front end of the laid-in pipes from the departure pit, have met with only partial success, since these attempts have involved undesirable additional procedures to remove the detector pipe and to fill the space formed therby with cement or the like, after the laying-in of the pipes is completed. Other difficulties occurring with the first-mentioned attempt are as follows: it is difficult to control the direction of advance of the laid-in pipes since the posture of the foremost, excavating point is unable to be detected and, hence, the operator must be skilled in ensuring that the pipes are advanced as straight as possible; (1) the screw conveyor rotated in the laid-in pipes tends to damage the inner surface of the pipes; (2) for this reason, the pipes to be laid in are in most cases limited to steel pipes since pipes of reinforced concrete are not suitable for this method; (3) where it is absolutely necessary to use the pipes of reinforced concrete, steel pipes should be placed in the reinforced concrete pipes in order to prevent the inner surface of the latter from being damaged by the rotating screw conveyor; and (4) there must be inserted the screw conveyor that fits with the internal diameter of the pipes, and this increases the cost of equipment because construction must have a wide variation in types and forms of screw conveyors to accommodate many different sizes of pipes to be laid in.
A difficulty attendant with the other attempt to press the pipes into the ground upon consolidation of soil is that since the degree of consolidation of soil is increased as the laid-in pipes increase in diameter, a large apparatus is necessary in order to obtain a jack pressure large enough to press pipes of corresponding sizes into the ground.
According to another method disclosed in Japanese Patent Publication No. 49-19767, small-diameter pilot pipes are first pressed into the ground by a hydrulic jack, and large-diameter pipes are led by the pilot pipes then laid in the ground. While this method is highly efficient, straight advancement of the laid-in pipes is not obtained because of the lack of control of the front end of the pilot head. The pilot pipes are followed by the large-diameter pipes which are laid-in upon consolidation of soil without excavating earth, and thus a relatively large consolidation pressure becomes necessary. This requires a large-sized apparatus. In short, this latter method shares the common deficiencies with the foregoing prior art attempt which makes use of consolidation of soil. While this method is highly efficient, it is not satisfactory to lay the pilot pipes precisely in position since the front end of the pilot pipes are uncontrolled. Furthermore, when large-diameter pipes are led by the laid-in pilot pipes and laid in the ground, a single conical head is employed for consolidation of soil in order to lay in the pipes. Therefore, there are required a large propulsion force and thus a large-sized apparatus.